Journal of Waterway, Port, Coastal, and Ocean Engineering

A robust and integrated interpretation of soil data from field investigations can provide valuable insights into the important role of soil deterioration following the installation of suction caissons. Therefore, a field experiment was conducted at a site in Frederikshavn to simulate laterally loaded suction caisson in a layered soil profile. The experiment was performed to validate our modeling approach and to systematically analyze the predictive capabilities of three classes of numerical predictions (Classes A, A1, and C). The Class A1 prediction focused primarily on the trajectory of the rotation center and the capacity of existing failure criteria to predict the bearing strength of shallow foundations under combined loading, despite differences in stress conditions, foundation geometries, and soil weakening due to the installation effect. On the other hand, the Class A prediction was carried out based on wished-in-place conditions. Failure envelopes within the Class C predictions were adopted to be scaled by the pure bearing capacities (given by intersections with the axes). Subsequently, the appropriateness of identical envelopes was examined here by employing three-dimensional finite-element analyses in the presence of the parabolic variations in soil stiffness with depth. An alternative macroelement model of varying failure surface parameters was also represented, which enables the bearing capacity of skirted foundations to be predicted for a wide range of embedment ratios and sand strength inhomogeneities.

Soft cliff (bluff) erosion during a storm is investigated using available wave basin data and a cross-shore numerical model for dune erosion. The measured cliff recession rates under oblique breaking waves for cliffs built of wet sand and a sand/clay mixture (90.8% sand) can be reproduced by a numerical model that is modified to account for sand loss associated with the alongshore gradient of longshore sand transport. The sand loss is affected by the beach material (concrete or sand) when the incident irregular waves break on the beach and cause sand transport seaward of the cliff toe with small depth. The effect of sediment cohesion on cliff erosion was examined using the numerical model extended to cohesive sediment containing sand. For cohesive sediment with weak resistance against wave action, the cliff recession rate was limited by the rate of sand removal by longshore and cross-shore sand transport. The recession rate decreased when the resistance of the cliff material exceeded a critical value. These findings will need to be verified using experimental and field data.

This paper demonstrated a new framework for port investment optimization that includes a three-stage process. First, a performance-based approach was applied to determine the margins of ship responses under external impacts and thereby establish operational safety policies. Second, a discrete event simulation model for assessing port performance was developed under various investment scenarios. A complex system of different underwater structures and port processes (such as access channel, water basin, anchorage area, tug usage, and mooring facility) was included in the model together with traffic rules and operational safety criteria. Finally, we generated optimal investment planning through cost strategy analysis. Our case study of Lien Chieu Port showed that the new framework is practical and effective in optimizing port investment by balancing between the port dimensions and cargo handling rates. The accuracy of the proposed approach could be further enhanced by introducing additional practical aspects of port operations into the simulation model.

This paper investigates a modular bucket foundation design developed for large offshore wind turbines. Instead of the regular round shape, the modular bucket consists of trapezoidal profiles bolted together and additional stiffeners attached to the inside skirt. The design is more cost-effective and gives much higher buckling resistance during installation compared with the standard round bucket, which serves as a reference point in the research. The paper includes both jacking installation and suction installation tests performed on a large-scale set-up at Aalborg University. The installations took place in sand of varying relative density. Each test consists of measurements for the applied force or suction and the excess pore pressure around the bucket skirt with increasing penetration depth until full installation. Results indicate that regardless of the significant increase in soil penetration resistance of modular bucket measured during jacking installation, the required suction for installation in different sand conditions is very similar for both models. The data are compared with a cone penetration test (CPT)-based method for the calculation of soil penetration resistance. The method is adjusted according to the experimental results supported by finite-element method analysis.

This paper presents the results of numerical investigation on the vertical bearing behavior of monopod caisson foundations embedded in sandy soils and supporting offshore wind turbines. The effects of embedment depth and internal soil plug were investigated. The magnitude of lateral soil deformation at the foundation tip is noted to increase with skirt length and it remains greater in comparison with that of an embedded solid foundation. The internal soil plug is found to have a cushioning effect during the transfer of superstructure load to the soil mass underneath the foundation tip. This leads to a reduction in the end-bearing component of vertical capacity when compared with that of an embedded solid foundation. The failure of the soil at the tip resembles the shape of an inverted parabola in the case of caisson foundation and that of an upright parabola for the embedded solid foundation. Based on the results, predictive expressions have been proposed to determine the ultimate vertical bearing capacity of the caisson foundation and its settlement for the range of geometry and superstructure load considered in the study.

Radar images can be employed to examine features of the ice surface and to determine ice drift. In the winter of 2012–2013, sea ice drift in the Bohai Sea was monitored using a marine radar system installed on an offshore platform in Liaodong Bay. Radar images were continuously captured across the 57-day ice season and processed to determine ice surface features and drift. The correlation between ice velocity and current and wind velocity is analyzed using a statistical approach. The results indicate that ice speed in the Bohai Sea mainly varies between 0.3 and 0.8 m/s, with a maximum value of 1.8 m/s. There was a dominating direction of 60° clockwise from the North, with the Coriolis force causing a 20° difference in drift direction. The probability distribution function shows that both sea ice and wind velocities follow the typical Weibull distribution.

A process-based parametric closure model for estimating cross-shore sediment transport (CST) rate has been developed for simulating long-term shoreline evolution. The formulations of this closure model include calculations of various subaqueous cross-shore transport components induced by waves, currents, and gravity. To better calculate asymmetrical near-bed orbital velocity that is a key to predict the cross-shore transport rate in the nearshore zone, a nonlinear wave-shape model is adopted. By formulating wave nonlinearity to cross-shore transport, this closure model can predict the net on- and offshore transport rates in response to shoreline accretion and erosion driven by waves and currents during low- and high-energetic conditions. This new capability for cross-shore shoreline change has been implemented into a one-line model, primarily driven by longshore sediment transport (LST). Calibration of model parameters and model validation were performed by simulating shoreline changes for a 5 km section of coastline in Duck, North Carolina, over a 14-year period from 2000 to 2013. The simulation results reproduced seasonal shoreline recoveries during low-energetic fair weather and also captured rapid retreats during storms. This shoreline model with inclusion of LST and CST has significantly improved the prediction accuracy of long-term shoreline changes at the study site. Impact analysis of a pier located within the domain reveals that this shoreline model with CST can better simulate sediment bypassing through the structure that depends on multiple local variables such as shoreline positions, updrift longshore transport, waves, and water levels. Therefore, this new shoreline model will facilitate long-term management of sediments and shoreline erosion and impact assessment of coastal structures.

The objective of the study is to present the main morphometric features of the inner sand bar of the nontidal Vistula Lagoon, to obtain actual data on the water exchange of the lagoon with the Baltic Sea, to compare the time variability of water exchange and regime-forming factors, and to estimate the volume of water exchange. The erosion was revealed for the inner sandy bar (comparing 2012 and 2019) which could be caused by regular dredging of the navigable canal (uptake the marine sediments feeding the bar). A sea-level rise of different origins guides impulse-fold inflow–outflow exchange of the lagoon with the sea estimated by direct current measurements in winter and spring. An inflow–outflow event is sustainable when the water level rises higher than 0.8 cm/h. Spring river input provides the shift in the equilibrium in water exchange toward outflow (by 10% in duration). The average rate of the inflow–outflow is 3.14 and 3.16; the maximum is 8.00 and 8.31 million m³ per hour. The average volumes per inflow–outflow events are 37 and 31 million m³. A simplified formula for calculating the exchange volume based on sea-level changes was recommended using a high correlation between them.